A solid-state magnetic memory device (MRAM) using a magnetoresistance effect (MR) film was proposed by L. J. Schwee in Proc. INTERMAG Conf. IEEE Trans. on Magn. Kyoto (1972) 405 and various types of MRAMs having a configuration including a word line that is a current line for generating recording magnetic field and a sense line for reading by the use of a MR film has been studied.
An example of such studies includes a study by A. V. Pohm et al. (IEEE Trans. on Magn. 28 (1992) 2356). These memory devices generally use a NiFe film, etc. having a MR change rate of about 2% and exhibiting an anisotropic MR effect (AMR). In such devices, there was a problem to improve the value of signals to be output.
There is a description of an artificial lattice film made of two magnetic films that are exchange-coupled to sandwich a non-magnetic film having a giant magnetoresistance effect (GMR) in M. N. Baibich et al., Phys. Rev. Lett. 61 (1988) 2472. Furthermore, a MRAM using such a GMR film has been proposed in K. T. M. Ranmuthu et al., IEEE Trans. on Magn. 29 (1993) 2593. However, although such a GMR film made of an antiferromagnetic exchange-coupling magnetic films has a large MR change rate, a larger magnetic field is required to be applied as compared with the above-mentioned AMR film. Therefore, there is a problem that a large current for recording and reading information is necessary.
In contrast to the above-mentioned exchange-coupling GMR film, as a nonexchange-coupling type GMR film, a spin bulb film using an antiferromagnetic film is described (B. Dieny et al., J. Magn. Magn. Mater. 93 (1991) 101). Furthermore, there is a description of a nonexchange-coupling type GMR film (spin bulb film) using a (semi)-hard magnetic film (H. Sakakima et al., Jpn. J. Appl. Phys. 33 (1994) L1668). This nonexchange-coupling type GMR film (spin bulb film) has the same low magnetic field as that of the AMR film and has a MR change rate larger than that of the AMR film. Furthermore, there is a description of a storage element having a nondestructive read out (NDRO) property in the MRAM using a spin bulb film of an antiferromagnetic film or a hard magnetic film (Y. Irie et al., Jpn. J. Appl. Phys. 34 (1995) L415). The present invention relates to this technology.
The non-magnetic film of the above-mentioned nonexchange-coupling type GMR film is a conductor film of Cu, etc. However, tunnel-type GMR films (TMR films) using an insulating film of oxide such as Al2O3 or MgO, etc. for a non-magnetic film have been studied increasingly and MRAMs using this TMR film have been proposed.
In the nonexchange-coupling type GMR film, it is known that the MR effect in the case where a current is allowed to flow perpendicular to the film surface (CPPMR) is larger than the MR effect in the case where a current is allowed to flow in parallel to the film surface (CIPMR). Furthermore, since the TMR film has a high impedance, by using the TMR film, a higher output can be expected.
However, when actually forming a magnetic memory or a magnetic head using a magnetoresistance element or a magnetoresistance storage element including such a spin bulb film, it is important to minimize variations in magnetoresistance properties of the element between elements and between processed wafers. In particular, it is important to restrict variations in a MR value (The MR value is defined by (Rap−Rp)/Rp, wherein Rp represents a resistance value when the magnetization directions of two ferromagnetic layers sandwiching a non-magnetic layer are placed in parallel with each other; and Rap represents a resistance value when the magnetization directions of two ferromagnetic layers sandwiching a non-magnetic layer are placed in non-parallel with each other. The MR resistance value becomes maximum when the resistance value is represented by Rap and the direction of magnetization of the two ferromagnetic layers are anti-parallel with each other.), a junction resistance value (The junction resistance value is represented generally by Rp×A, wherein A represents a junction area of elements) and variations in a bias dependency of the MR value and the junction resistance value.
When the size of the element becomes of a sub-micron order as a result of making the element to be fine, variations in the junction resistance value become significant. This is because the reduction of the junction area of the elements makes an electric contact between an element and an electrode material substantially difficult, thus making the distribution of the state of the electric contact on the junction surface to be uniform.
With the foregoing in mind, it is an object of the present invention to restrict variations in the magnetoresistance properties such as the MR value, the junction resistance value, etc. in a fine-patterned magnetoresistance element, magnetoresistance storage element and magnetic memory.